The reasons for fasting are: 1. After eating, the gallbladder will contract, bile excretion and bile concentration will lead to thickening of the gallbladder wall, unclear structure of the gallbladder wall, shrinkage of the gallbladder cavity, poor sound transmission of the gallbladder and other false positive results, as well as omission of the abnormal echogenicity of the gallbladder wall and gallbladder cavity resulting in missed diagnosis. In short, after a meal, the observation of the gallbladder is extremely affected, especially when eating meat, eggs and dairy foods.2. After a meal, the abdominal cavity gas increases, and the ultrasound encounters gas reflection resulting in serious attenuation of acoustic energy, and the deep structure of the gas is not displayed, which affects the ultrasound image display of the liver and pancreas, so it is necessary to fast for more than eight hours to do ultrasound examinations of these parts, and the spleen ultrasound alone can be done without fasting. In addition, for ultrasound of liver, gallbladder, pancreas and spleen, it is recommended to go in the morning for better results, because the gas in the abdominal cavity itself will increase in the afternoon.